<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			.box1{
				width:1200px;
				margin: 0 auto;
				background-color: pink;
			}
			.box2{
				width: 300px;
				height: 300px;
				background-color: green;
				float: left;
			}
			.box3{
				width: 300px;
				height: 300px;
				background-color: blue;
				float: left;
			}
			.box4{
				width: 300px;
				height: 300px;
				background-color: yellow;
			}
			.box5{
				clear: both;
				width: 1200px;
				margin: 0 auto;
				background-color: red;
			}
		</style>
	</head>
	<body>
		<div class="box1">
			<div class="box2"></div>
			<div class="box3"></div>
		</div>
		<div class="box5">
			<div class="box4"></div>
		</div>
	</body>
</html>